Suspension process for the polymerization of vinylidene aromatic hydrocar-bons having rubbery conjugated 1, 3-diene polymers dissolved therein



United States Patent ice Dec. 2,

SUSPENSION PROCESS FOR THE POLYMERIZA- TION (BF VINYLHDENE AROMATICHYDRQCAR- BONS HAVING RUBBERY CONJUGATED 1,3-DI- ENE POLYMERS DISSOLVEDTHEREIN Alvin Stein and Robert L. Walter, Springfield, Mass, assignorsto Monsanto Chemical Company, St. Louis, Mo., a corporation of DelawareN0 Drawing. Application April 1, 1957 Serial No. 649,596

6 Claims. (Cl. 260-455) The present invention relates to an improvedprocess for polymerizing vinylidene aromatic hydrocarbon andring-halogenated vinylidene aromatic hydrocarbon monomers having rubberyconjugated 1,3-diene polymers dissolved therein by a suspensionpolymerization process. In the subsequent description of this invention,for the sake of brevity, the vinylidene aromatic hydrocarbon orring-halogenated vinylidene aromatic hydrocarbon monomer solution of therubbery conjugated 1,3-diene polymer frequently will be referred tosimply as the vinylidene aromatic hydrocarbon solution or the vinylidenemonomer solution.

Processes for preparing polymers from vinylidene aromatic hydrocarbon orring-halogenated vinylidene aromatic hydrocarbon monomers having rubberyconjugated 1,3-diene polymers dissolved therein by suspensionpolymerization processes are known. See the co-pending application ofJohn B. Ott, Serial No. 573,074, filed March 22, 1956, and our twoco-pending applications Serial No. 649,594, and Serial No. 649,595, bothfiled of even date herewith. solution is dispersed and polymerized in anaqueous medium containing as the dispersing agent either certainwater-soluble interpolymers of 93.5-98.5 mol percent of an acidicmonomer of the group consisting of acrylic acid, methacrylic acid, andmixtures thereof and, correspondingly, 6.54.5 mol percent of a monomerof the group consisting of 2-ethylhexyl acrylate, 2-ethylhexylmethacrylate and mixtures thereof or a binary mixture of such awater-soluble interpolymer and a bis(sulfoaryl) alkane. In the preferredembodiments of the previously described methods, the vinylidene monomersolution is partially polymerized before being dispersed in the aqueousmedium containing the dispersing agent.

There are minor difliculties associated with the abovedescribedprocesses, which difliculties, although not atfecting the quality of thepolymer product obtained, do increase the cost of manufacturing thepolymer. The first of these difiiculties is that a substantialpercentage of the polymer particles formed in the polymerization floatin the aqueous dispersing medium. These floating particles cannot beseparated from the aqueous dispersing medium by centrifuging incontiguous centrifuges of the popular solid bowl type, which for manyreasons is the most desirable method for recovering the polymerparticles. The second ditficulty is that the polymer particles occludesubstantial quantities of water and are costly'to dry.

It is an object of this invention to provide an improved process for thesuspension polymerization of vinylidene aromatic hydrocarbon andring-halogenated vinylidene aromatic hydrocarbon monomers having arubbery conjugated 1,3-diene polymer dissolved therein.

Another object of this invention is to provide an improved process forthe suspension polymerization of vi- In these processes, the vinylidenemonomer nylidene aromatic hydrocarbon and ring-halogenated vinylidenearomatic hydrocarbon monomers having a rubbery conjugated 1,3-dienepolymer dissolved therein in which substantially all of the polymerparticles will sink in the aqueous dispersing medium.

A further object of this invention is to provide an improved process ofthe suspension polymerization of vinylidene aromatic hydrocarbon andring-halogenated vinylidene aromatic hydrocarbon monomers having arubbery conjugated 1,3-diene polymer dissolved therein in which thepolymer particles will occlude relatively small quantities of water.

Other objects and advantages of this invention will be apparent from thefollowing detailed description thereof.-

The above and other objects are obtained by (1) agitating and heating amixture of water and a partially poly merized solution of a rubberyconjugated 1,3-diene polymer in a vinylidene monomer of the groupconsisting of a vinylidene aromatic hydrocarbon monomer, aringhalogenated vinylidene aromatic hydrocarbon monomer and mixturesthereof to a temperature of at least about C. in the absence of adispersing agent, (2) adding to said mixture of water and partiallypolymerized vinylidene monomer solution, as a dispersing agent, either awater-soluble interpolymer consisting of 93.5-98.5 mol percent of anacidic monomer of the group consisting of acrylic acid, methacrylic acidand mixtures thereof, and, correspondingly, 6.5-1.5 mol percent of amonomer of the group consisting of Z-ethylhexyl acrylate, Z-ethylhexylmethacrylate and mixtures thereof or a binary mixture of such awater-soluble interpolymer and a bis(sulfoaryl) alkane and (3)continuing to agitate and heat said mixture of water and partiallypolymerized vinylidene monomer solution until the vinylidene monomer issubstantially completely polymerized. The partially polymerized solutionof the rubbery conjugated 1,3-diene polymer in the vinylidene monomeremployed in the process is characterized by (1) having at least about15% of the monomeric constituents of the vinylidene monomer solutionpolymerized and (2) having a viscosity of at least about 40 poises at 40C.

The following examples are set forth to illustrate more clearly theprinciple and practice of this invention to those skilled in the art.Where parts are mentioned, they are parts by weight.

Example I .To a glass lined, stirred autoclave are charged 100 parts offreshly distilled water and 100 parts of a partially polymerized styrenesolution of a rubbery butadienestyrene interpolymer. The styrenesolution contains 6 parts of an interpolymer of 75% butadiene and 25%styrene dissolved in 94 parts of styrene monomer together with 005 partof ditertiary butyl peroxide, 0.3 part of an anti-oxidant, 0.1 part of acommercial C mercaptan modifier and 2.0 parts of a refined hydrocarbonoil lubricant. Thirty-three percent of the styrene monomer ispolymerized and the partially polymerized stcgluton has a viscosity ofapproximately 'poises at The reaction mixture is placed under nitrogenpressure and agitated and heated to 110 C. for 15 minutes and there isthen charged thereto 20 parts of water having dissolved therein 0.25part of the sodium salt of bis(sulfonaphthyl) methane, 0.1 part ofcalcium chloride and.0.l3 part of an interpolymer of 95.5 mol percent ofacrylic acid and 4.5 mol percent of 2-ethylhexyl acrylate which has aspecific viscosity of about 4.0 as determined in a 1% solution at 25 C.Thereafter, the reaction mixture is agitated and heated for 3 hours atC. and 5 hours at C. The polymer is obtained in substantiallyquantitative yield in the form of homogeneous small spherical beads.Essentially all of the polymer particles obtained 3 .are heavier. thanwaterand can be separated from the aqueous,dispersingmedium in.acontinuous .solid bowl type centrifuge. The water content of therecovered polymer particles is less than 7%.

Comparative. Example I Example I is repeated except that before chargingthe dispersing, agents tothesystem, the water and the partiallypolymerized styrene monomer solution of the rubbery butadiene-styreneinterpolymer are heated for minutes at- 105 C. in lieu of the 110". C.employed in Example I. She-polymer obtained in this example containsapproximately 28 weight percent of particles'which float in the aqueousdispersing medium. Thesefloating polymer par- .ticles cannot beseparated .fromuthe'aqueous dispersing medium in a continuous -solidbowl type centrifuge.

The moisture contentof the-polymer particles is 9%.

Comparative Example 11 Comparative Example I is repeated except thatbefore charging. the dispersing agents to the system,'the water and thepartially polymerized styrene monomer solution of the rubberybutadiene-styrene polymer are heated for 15 minutes at 90 C. Thirty-fivepercent of the polymer particles float in the aqueous dispersing mediumand cannot be separated therefrom in a continuous solid bowl typecentrifuge. The moisture content of the polymer is 14%.

Example 11 Example I is repeated except that the polymerizablecomposition employed comprises parts of an interpolymer of 75% butadieneand styrene dissolved in 80 parts of styrene monomer. Comparable resultsare obtained.

Example Ill -Example I is repeated except that 6 parts of aninterpolymer of 75 butadiene and 25% styrene are dissolved in a monomermixture consisting of 84 parts styrene monomer and 10 parts alphamethylstyrene monomer. Comparable results are obtained.

Example IV Example I is repeated except that 6 parts of an interpolymerof 75 butadiene and 25% styrene are dissolved in a monomer mixtureconsistingof 66 parts styrene monomer and 28 parts acrylonitrilemonomer. Comparable results are obtained.

In the initial step of the invention, water and a partially polymerizedvinylidene monomer solution of critical characteristics are agitated andheated to a temperature of-at least 110 C. in the absence of dispersingagents. The partially polymerized vinylidene monomer solution employedis characterized in that at least about 15% of the original monomericcomponents of the solution are polymerized and the solution has aviscosity of at least 40 poises at 40 C. In carrying out this initialstepof the process, it is customary to charge the entire quantity ofwater that will be employed in the suspension polymerization step,except for a small quantity of water that may be withheld and employedas a solvent for the dis persing agent that is ultimately added to thesystem. In nearly all cases, the quantity ofwater employed shouldconstitute at least about 35% or more preferably at least 50% of theweight of the partially polymerized vinylidene monomer solution. Theperiod of contact between the -vinylidcne monomer solution and the watermay be quite brief as very noticeable benefits are obtained when thisperiod is as short as about 10 minutes.

In one embodiment of the invention, the vinylidene monomer solution ispartially polymerized en masse before being employed in the process ofthis invention. In an alternate embodiment of the invention, theunpolymerized vinylidene monomer solution and water are charged to areactor. and heated and agitated until the vinylidene monomer solutionhas beenpartially polymerized to the extent previously indicated. Ifthis polymerization is carried out at a temperature of C. or higher, thedispersing agent may be added to the system as soon as the requisiteconversion of the vinylidene monomer solution is obtained. If, however,this initial polymerization is carried out at a temperature of less than110 C., the mixture of water and the partially polymerized vinylidenemonomer solution should be agitated and heated for a short period oftime at a temperature of at least 110 C. before the dispersing agent isadded to the system.

After the initial step of agitating and heating the water and thepartially polymerized vinylidene monomer solution in the absence ofdispersing agents is completed, a dispersing agent of a restricted classis added to the aqueous phase and the polymerization is completed in theusual manner. The dispersing agents employed are watersolubleinterpolymers of an acidic monomer of the group consisting of acrylicacid, methacrylic acid and mixtures thereof and a monomer ofthe groupconsisting of 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate andmixtures thereof. For the purposes of thisinvention, such interpolymersare considered to be water-soluble if 0.5 part of the interpolymerwill'dissolve in 99.5 parts of Water at 25 C. Such interpolymers shouldcontain 1.5-6.5 mol percent and preferably 2.0-5.0 mol percent of the2-ethylhexyl ester with the balance of the interpolymer being the acidicmonomer. For reasons of both cost and performance, it is 7 preferred toemploy interpolymers of acrylic acid and 2-ethylhexyl acrylate.

The dispersing action of the water-soluble interpolymers is affected butslightly by wide variations in molecular weight. The preferreddispersing agents, however, have specific viscosities of at least 0.1when methacrylic acid is the acidic monomer included in the interpolymerand at least about 0.8 when acrylic acid is the acidic monomer includedin the interpolymer. Both of the above specific viscosity values aredetermined in 1% solutions in water at 25 C. in accordance with thewell-known formula:

Solution viscosity-solvent; viscosity Solvent viscosity Specificviscosityagent is necessary, 0.021.0% and more particularly 0.05-

0.5% based upon the amount of water used is usually sufficient.Frequently, there is found to be an optimum amount of dispersing agentto be employed for obtaininga minimum particlesize and amounts ofdispersing agent above or below this optimum amount produce polymershaving a larger particle size. It is usually preferred to employ thesmallest .amount of dispersing agent that will produce polymers of thedesired particle size.

It is possible and sometimes desirable to employ two or more differentdispersing agents in the process of this invention, at least one of saiddispersing agents being a water-soluble interpolymer of the typepreviously described. Particularly good results are obtained with binarydispersing'agent systems in which the second dispersing agent is abis(sulfoaryl) alkane or preferably a water-soluble salt thereof such asan alkali metal, ammonium oramine salt. Typical. examples of such bis-.(sulforayl) alkanes include.bis(sulfophenyl) methane, bis(sulfotolyl)methane, bis(sulfonaphthyl) methane, 1,1- bis(sulfopheny1) ethane,2,2ebis(sulfonaphthyl) propane,

etc. Such bis(sulfoary1) alkanes are normally employed in concentrationsof the same order of magnitude as the Water-soluble interpolymersuspending agents.

In carrying out the suspension polymerization step, it is usuallypreferred to maintain the pH of the aqueous dispersing medium belowabout 7.0. The water-soluble interpolymer dispersing agents containcarboxyl groups and, when employed at the preferred levels, will lowerthe pH of the aqueous dispersing medium to the approximate range of3.0-4.0, which is close to the optimum pH. If desired, small quantitiesof inorganic salts may be included in the aqueous medium to suppressemulsification of the polymer.

The compositions which may be polymerized by the method of thisinvention comprise solutions of a rubbery conjugated 1,3-diene polymerin a vinylidene aromatic hydrocarbon or ring-halogenated vinylidenearomatic hydrocarbon monomer or a monomer mixture consistingpredominantly of a vinylidene aromatic hydrocarbon or a ring-halogenatedvinylidene aromatic hydrocarbon. Although vinylidene monomer solutionscontaining minor amounts of a rubbery conjugated 1,3-diene polymer, e.g., less than 1%, may be polymerized by the process of the invention,the optimum value of the process is obtained in polymerizing vinylidenemonomer solutions containing substantial amounts of the rubberyconjugated 1,3- diene polymer, e. g., more than 2% and more especiallymore than 5% of the rubbery conjugated 1,3-diene polymer. The processhas been employed successfully to polymerize styrene monomer having asmuch as 25 weight percent of a rubbery butadiene-styrene interpolymerdissolved therein. The upper limit on the rubbery conjugated 1,3-dienepolymer content will be set primarily by the viscosity of the partiallypolymerized vinylidene monomer solution.

The rubbery conjugated 1,3-diene polymer component of the polymerizablemixture may be essentially any rubbery conjugated 1,3-diene polymerhaving a brittle temperature of 0 C. or less, said brittle temperaturebeing determined by ASTM Test procedure D746-52T. Typical examples ofsuch polymers include natural rubber itself, synthetic polyisoprene,polybutadiene, interpolymers of butadiene and/ or isoprene with styrene,acrylonitrile, acrylate esters, etc.

The monomeric component of the polymerizable mixture may consist of (l)a vinylidene aromatic hydrocarbon or ring-halogenated vinylidenearomatic hydrocarbon such as styrene; vinyl naphthalene;ring-substituted alkylstyrenes, e. g., vinyl toluene, o-ethylstyrene,p-ethyl styrene, 2,4-dimethylstyrene, etc.; ring-substitutedhalostyrenes, e. g., o-chlorostyrene, p-chlorostyrene, o-bromostyrene,2,4-dichlorostyrene, etc.; ring-substituted alkyl-, ring-substitutedhalostyrenes, e. g., 2-chloro-2-methylstyrene,2,6-dichloro-4-methylstyrene, etc.; (2) a mixture of two or morevinylidene aromatic hydrocarbons or a ring-halogenated vinylidenearomatic hydrocarbon, which mixture may include a vinylidene aromatichydrocarbon which will not readily homopolymerize, e. g.,alpha-methylstyrene or (3) a mixture of a major amount of a vinylidenearomatic hydrocarbon or ring-halogenated vinylidene aromatic hydrocarbonwith a minor amount of a vinylidene monomer interpolymerizabletherewith. Examples of such interpolymerizable vinylidene monomersinclude conjugated 1,3-dienes, e. g., butadiene, isoprene, etc.,alpha,beta-unsaturatcd monobasic acids and derivatives thereof, e. g.,acrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate,2-ethylhexyl acrylate, and the corresponding esters of methacrylic acid,acrylamide, methacrylamide, acrylonitrile, methacrylonitrile, etc.

In addition to the rubbery conjugated 1,3-diene polymer and thevinylidene aromatic hydrocarbon or ring halogenated vinylidene aromatichydrocarbon monomer, the polymerizable mixtures may also contain freeradical generating polymerization initiators, anti-oxidants,plasticizers, heat and light stabilizers, polymerization modifiers,colorants, etc.

The above descriptions and particularly the examples are set forth byway of illustration only. Many other variations and modificationsthereof will be apparent to those skilled in the art and can be madewithout departing from the spirit and scope of the invention hereindescribed.

What is claimed is:

1. A process for preparing polymerization products in granular formwhich comprises (1) agitating and heating a mixture of at least about 35parts of water and parts of a partially polymerized solution of arubbery conjugated 1,3-diene polymer in a vinylidene monomer of thegroup consisting of a vinylidene aromatic hydrocarbon monomer, aring-halogenated vinylidene aromatic hydrocarbon monomer and mixturesthereof to a temperature of at least about C., in absence of adispersing agent, (2) adding to said mixture of water and partiallypolymerized vinylidene aromatic hydrocarbon monomer solution, as adispersing agent, a water-soluble interpolymer consisting of 93.5-98.5mol percent of an acidic monomer of the group consisting of acrylicacid, methacrylic acid and mixtures thereof, and, correspondingly,6.5-1.5 mol percent of a monomer of the group consisting of 2-ethy1hexylacrylate, 2-ethylhexy1 methacrylate and mixtures thereof, and (3)continuing to agitate and heat said water and partially polymerizedvinylidene aromatic hydrocarbon monomer solution until said vinylidenearomatic hydrocarbon monomer is substantially completely polymerized;the vinylidene aromatic hydrocarbon monomer solution employed in step 1)being characterized by the fact that at least about 15% of the monomericconstituents of the vinylidene aromatic hydrocarbon monomer solutionhave been polymerized and that said partially polymerized vinylidenearomatic hydrocarbon monomer solution has a viscosity of at least about40 poises at 40 C.

2. A process as in claim 1 in which the dispersing agent added in step(2) is a water-soluble interpolymer of acrylic acid and Z-ethylhexylacrylate.

3. A process as in claim 2 in which the rubbery polymer of a conjugated1,3-diene is an interpolymer of 1,3- butadiene and styrene.

4. A process as in claim 2 in which the monomer employed comprises amixture of a major amount of styrene and a minor amount of alphamethylstyrene.

5. A process as in claim 2 in which the monomer employed comprises amixture of a major amount of styrene and a minor amount ofacrylonitrile.

6. A process as in claim 2 in which the monomer em ployed is styrene.

No references cited.

1. A PROCESS FOR PREPARING POLYMERIZATION PRODUCTS IN GRANULAR FORM WHICH COMPRISES (1) AGITATING AND HEATING A MIXTURE OF AT LEAST ABOUT 35 PARTS OF WATER AND 100 PARTS OF A PARTIALLY POLYMERIZED SOLUTION OF A RUBBERY CONJUGATED 1,3-DIENE POLYMER IN A VINYLIDENE MONOMER OF THE GROUP CONSISTING OF VINYLIDENE AROMATIC HYDROCARBON MONOMER, A RING-HALOGENATED VINYLIDENE AROMATIC HYDROCARBON MONOMER AND MIXTURES THEREOF TO A TEMPERATURE OF AT LEAST ABOUT 110*C., IN THE ABSENCE OF A DISPERSING AGENT, (2) ADDING TO SAID MIXTURE OF WATER AND PARTIALLY POLYMERIZED VINYLIDENE AROMATIC HYDROCARBON MONOMER SOLUTION, AS A DISPERSING AGENT, A WATER-SOLUBLE INTERPOLYMER CONSISTINGT OF 93.5-98.5 MOL PERCENT OF AN ACIDIC MONOMER OF THE GROUP CONSISTING OF ACRYLIC ACID, METHACRYLIC ACID AND MIXTURES THEREOF, AND, CORRESPONDINGLY, 6.5-1.5 MOL PERCENT OF A MONOMER OF THE GROUP CONSISTING OF 2-ETHYLEXYL ACRYLATE, 2-ETHYLHEXY METHACRYLATE AND MIXTURES THEREOF, AND (3) CONTINUING TO AGITATE AND HEAT SAID WATER AND PARTIALLY POLYMERIZED VINYLIDENE AROMATIC HYDROCARBON MONOMER SOLUTION UNTIL SAID VINYLIDENE AROMATIC HYDROCARBON MONOMER IS SUBSTANTIALLY COMPLETELY POLYMERIZED; THE VINYLIDENE AROMATIC HYDROCARBON MONOMER SOLUTION EMPLOYED IN STEP (1) BEING CHARACTERIZED BY THE FACT THAT AT LEAST ABOUT 15% OF THE MONOMERIC CONSTITUENTS OF THE VINYLIDENEE AROMATIC HYDROCARBON MONOMER SOLUTION HAVE BEEN POLYMERIZED AND THAT SAID PARTIALLY POLYMERIZED VINYLIDENE AROMATIC HYDROCARBON MONOMER SOLUTION HAS A VISCOSITY OF AT LEAST ABOUT 40 POISES AT 40*C. 